The interior of a commercial aircraft, such as a passenger aircraft, is divided into at least one passenger space or cabin and a loading space for luggage and/or freight. These spaces, especially the passenger cabin, are divided into temperature zones which are controllable in a closed loop or open loop manner independently of one another. Official regulations require that a minimal fresh air volume is introduced into the passenger cabin per passenger during defined time durations. The fresh air is provided by feeding highly compressed hot fresh air with one or more high pressure blowers for a high pressure air distribution in the aircraft. The highly compressed fresh air passes from a high pressure source through a closed loop flow volume control valve and enters from the exit of the valve into an air-conditioning system which decompresses and cools the fresh air to a pressure and temperature suitable for use in the aircraft. The so-conditioned air exiting from the air-conditioning system is introduced into a low pressure air distribution system including an air mixer, wherein the air-conditioned air is mixed with a portion of used cabin air. The portion of used cabin air is withdrawn with a low pressure blower or ventilator from the passenger cabin and supplied to the mixer which also receives the fresh conditioned air. The mixed air is then supplied to one or several temperature zones in the aircraft, whereby a so-called "trim system" assures a closed loop temperature control individually for the several temperature zones in the aircraft. According to European Patent Application EPO 537,296 B1 the trim system includes a controller for monitoring and for controlling the feedback control values or signals.
It is further known that the air-conditioning or cooling "packs" in an aircraft can produce air temperatures below the water freezing point, especially when the humidity in the air is high. Thus, it is necessary that humidity contained in the air supplied to the air-conditioning system in an aircraft is first removed in order to prevent the formation of ice and/or snow in the air conditioner, in the air ducts or pipes or air conduits to thereby assure the required freeze up protection. This freeze up protection limits the possible cooling capacity of the air-conditioning packs depending on the moisture or water content of the incoming air. Freeze-ups are trouble sources for the system because flow cross-sectional areas may be reduced by such freeze-ups, particularly in flow critical locations within the system, such as pipes and structural system components, for example valves. A complete clogging due to freeze-ups must be prevented because air pipes could burst and cause a catastrophe in an aircraft. Even reductions in the flow cross-sectional area due to partial freeze-up must be avoided because noise caused by air flowing through reduced cross-sectional flow areas impairs the passenger comfort. Partial freeze-ups causing unwanted noise have a tendency to occur when the fresh air supply has been reduced to the minimally permissible volume, whereby the temperature of the output air from the air conditioner may sink below the freezing point of water, while at the same time, the output air still contains a remainder moisture content which reduces the cooling capacity of the air-conditioning system. German Patent Publication DE 3,330,556 C2 discloses that a freeze-up in the recirculation of the turbine air can be minimized by recirculating cabin air.
The prior art still leaves room for improvement, especially with regard to avoiding or preventing freeze-ups in the air flow cross-sectional area of the air pipes, ducts, conduits of the low pressure air distribution system while simultaneously assuring a minimal admixture of fresh air to the air recirculated from the aircraft cabin to produce mixed air to be supplied into the cabin.